Color separation device, imaging optical engine, and projection apparatus

ABSTRACT

A color separation device according to the present invention comprises a first color separation member having a first polarization direction changing element and a second polarization direction changing element, and a first polarization separation element, and a second color separation member having a second polarization separation element. The first color separation member may be configured from a color separation function element and a polarization direction changing element. Linearly polarized light being made incident on the first color separation member at an angle of approximately 45 degrees so as to separate the light into reflected light and transmitted light, both lights having different colors and one of the different colors corresponding to one of three colors, and one of the lights being made incident on the second color separation member so as to separate the one of the lights into further reflected light and further transmitted light, both further reflected light and further transmitted light corresponding to the other two of the three colors, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a color separation devicethat separates linearly polarized white light into three primary colors,an imaging optical engine that generates a color image (color imagelight) using such color separation device, and a projection apparatususing such imaging optical engine.

2. Description of the Related Art

Recently, “liquid crystal projectors” that project images displayed onliquid crystal panels, etc. onto display media such as a screen, etc. ina larger scale are widely used for displaying video reproduction imagesand computer data, etc. In particular, “three-panel liquid crystalprojectors” used for a color image presentation are widely used sincethe color images can be displayed thereby with a high resolution.

The liquid crystal panels are generally referred to as “light valves”and they can change the polarization direction of output light withrespect to linearly polarized input light on a pixel basis.

Meanwhile, “wavelength selective retarders” that can provide “ahalf-wavelength retardation” between ordinary light and extraordinarylight in the linearly polarized light in a desired waveband are known.The half-wavelength retardation can be provided to “light in thewaveband that can be arbitrarily determined as a design condition.”Therefore, for example, when p-polarized light is made incident on thewavelength selective retarders, only certain waveband is s-polarized andthe other wavebands are remained p-polarized.

Recently, three-panel liquid crystal projectors using such wavelengthselective retarders have been proposed (see for example, JapaneseLaid-Open Patent Application No. 2000-284228).

FIG. 1 shows a schematic configuration of one example of a projectionapparatus mounted on a three-panel liquid crystal projector according tothe related art. The projection apparatus includes a light source part 1having a lamp 11 and a polarization plate 12, a color separation part 2having a polarization beam splitter 21 for color separation, anarrowband phase difference plate (wavelength selective retarder) 22 forthe red component, and a narrowband phase difference plate (wavelengthselective retarder) 23 for the blue component, a GB (green/bluecomponents) modification part 3 having a polarization beam splitter 31for the green and blue components, a liquid crystal panel (reflectiveoptical modulator) 32 for the blue component, and a liquid crystal panel(reflective optical modulator) 33 for the green component, a redcomponent modification part 4 having a polarization beam splitter 41 forthe red component and a liquid crystal panel (reflective opticalmodulator) 42 for the red component, a color combining part 5 having apolarization beam splitter 51 for color combining and a narrowband phasedifference plate (wavelength selective retarder) 52 for the greencomponent, and a projection optical system part 6.

In such a three-panel liquid crystal projector, the linearly polarizedwhite light is incident on the first wavelength selective retarder(described as “narrowband phase difference plate” in the cited document)22. Among the lights that passed through the first wavelength selectiveretarder 22, waveband light (A) having its polarization directionchanged and waveband light (NA) not having its polarization directionchanged are separated to have different optical paths respectively bythe polarization beam splitter 21. The waveband light (A) having itspolarization direction changed is applied to the first light valve(mentioned as “reflective light modulator” in the cited document) 42.The waveband light (NA) not having its polarization direction changed isfurther separated into waveband light (B) and waveband light (C), eachof the waveband lights (B, C) having a different primary color, by thesecond wavelength selective retarder 23 and the polarization beamsplitter 31. The waveband light (B) is applied to the second light valve32 and the waveband light (C) is applied to the third light valve 33.After combining image lights (LB, LC) that are modulated according toimage signals and which are reflected from the second light valve 32 andthe third light valve 33 by the second polarization beam splitter 31,the polarization directions of the image lights (LB, LC) are madecoincident with one another by the third waveband selective retarder 52.Whereas, image light reflected from the first light valve 42 (LA) iscombined with the previously combined image lights LB, LC by the thirdpolarization beam splitter 51. The combined color image light isincident on the projection optical system 6, which projects the combinedcolor image light onto a screen (not shown) so as to display a colorimage.

As for the wavelength selective retarders used in such a projectionapparatus, an element formed by stacking phase difference plates thatmake use of double reflection of light disclosed in Japanese patent No.130537 (Japanese Laid-Open Application No. 11-504441) may be used.

In the projection apparatus disclosed in the Japanese Laid-Open PatentApplication No. 2000-284228, image light formed by liquid crystal panels(light valves) for respective primary colors are directed to aprojection lens by passing through polarization beam prisms or dichroicprisms, etc. In such a projection apparatus, the projection lens isdesigned so that the projection magnification, etc. with respect to eachliquid crystal panel are precisely controlled in order to make the backfocal distance from the projection lens to each liquid crystal panelequal. However, when imaging optical paths having wavelength selectiveretarders made from materials that are different from glass material ofthe prisms, in other words, made from material having refraction indicesdifferent from that of the prism, and imaging optical paths withoutthose wavelength selective retarders are used together, color imagequality is adversely affected. In addition, it is difficult to devise adesign for the projection lens that keeps a high level of performance.

Further, as another example of the related art, a reflective liquidcrystal projector device is proposed in Japanese Laid-Open PatentApplication No. 2001-281614. The proposed projector device ischaracterized in that an optical engine part in a projection unit of theproposed projector device is integrally configured, as a colorseparation/combining part, from a first color separation part, an entryand exit directions change part, a second color separation part, a colorcombining part, and a support part and in that a polarizationdirection-rotating member (narrowband phase difference platecorresponding to the wavelength selective retarder) is stacked onto thecolor separation parts. The projection unit of the proposed projectordevice is configured from, for example, as shown in FIG. 2, a lightsource part 301 having a lamp 311 and a polarization plate 312, a colorseparation part 302 having a polarization separation surface 321 forcolor separation, a narrowband phase difference plate 322 for redcomponent, and a narrowband phase difference plate 323 for bluecomponent, a GB (green/blue components) modulation part 303 having apolarization separation surface 331 for green component and bluecomponent, a liquid crystal panel 332 for the green component, and aliquid crystal panel 333 for the blue component, and a R (red component)modulation part 304 having a polarization separation surface 341 for thered component and a liquid crystal panel 342 for the red component, acolor combining part 305 having a polarization separation surface 351for color combining and a narrowband phase difference plate 352 for theblue component, a positioning support 306, and a projection opticalsystem 307.

However, in such projector device configured as shown in FIG. 2, atleast three sets of polarization direction-rotating members (narrowbandphase difference plates) 322, 323, 352 are necessary. Not only does itcause an increase in cost due to an increase in the number of componentsbut it may also generate a risk of reducing the performance level of theprojector device when, for example, assembly error accumulates duringmanufacture. Also, as shown in FIG. 2, image light from the liquidcrystal panel 332 for the green component or the liquid crystal panel333 for the blue component passes through the polarizationdirection-rotating member (narrowband phase difference plate for theblue component) 352 at an angle of 45 degrees. This means that the imagelight passes through the polarization direction-rotating member 352 inthe form of a parallel plate diagonally and this leads to deviation inthe optical path, etc. Further, since the image light formed by theliquid crystal panel 342 for the red component dose not pass through anyof the polarization direction-rotating members, optical path length ofthe red image light and that of blue and green image light aredifferent, and this leads to quality reduction in the composite colorimage.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea color separation device, by which it is possible to perform colorseparation where the polarization directions are made coincident withone another by suitably combining a wavelength selective retarder and apolarization separation element or a color separation function element.

A further object of the present invention is to provide an imagingoptical engine that has imaging optical path length for respectivecolors, which optical paths lie between respective light valves and acolor combining part, coincide with one another by using such colorseparation device and thus eliminating the necessity of providing thewavelength selective retarder in the imaging optical path.

A further object of the present invention is to provide a projectionapparatus using such an imaging optical engine, which projectionapparatus can provide high quality color images.

A further object of the present invention is to provide an imagingoptical engine and a projection apparatus, both having a high quality,by effectively improving the contrast of the color images.

A further object of the present invention is to provide an adjustableprojection apparatus, which can adapt to a case when priority is givento the brightness over the contrast of the color image according to auser's intended purpose.

A further object of the present invention is to provide a projectionapparatus, which has a configuration that prevents quality reduction ofthe combined color image by realizing an optical system that has noinclined wavelength selective retarders in optical paths for projectingthe images formed at respective light valves.

According to the present invention, there is provided a color separationdevice of a first type that comprises a first color separation memberhaving a first polarization direction changing element, a secondpolarization direction changing element, each of the polarizationdirection changing element changing polarization directions of differentpredetermined wavebands of incident light in different modes, and afirst polarization separation element that reflects or transmits theincident light according to the polarization directions of the incidentlight, and a second color separation member having a second polarizationseparation element. Linearly polarized light being made incident on thefirst color separation member at an angle of approximately 45 degrees soas to separate the linearly polarized light into reflected light andtransmitted light, both reflected light and transmitted light havingdifferent colors and one of the different colors corresponding to one ofthree colors, and one of the reflected light and the transmitted lightbeing made incident on the second color separation member so as toseparate one of the reflected light and the transmitted light intofurther reflected light and further transmitted light, both furtherreflected light and further transmitted light corresponding to the othertwo of the three colors, respectively.

In such a color separation device of the first type according to thepresent invention, the first polarization separation element may besupported between the first polarization direction changing element andthe second polarization direction changing element.

In such a color separation device of the first type according to thepresent invention, the linearly polarized light may be made incident onand may pass through the first polarization direction changing elementat an angle of approximately 45 degrees so as to separate the linearlypolarized light into waveband light having its polarization directionchanged and waveband light not having its polarization directionchanged; the waveband light having its polarization direction changed bythe first polarization direction changing element may be reflected fromthe first polarization separation element as the reflected lightcorresponding to one of the three colors; the waveband light not havingits polarization direction changed by the first polarization directionchanging element may pass through the first polarization separationelement as the transmitted light; the reflected light may be separatedfrom the transmitted light by passing through the first polarizationdirection changing element again; the transmitted light may pass throughthe second polarization direction changing element that is provided inparallel with the first polarization direction changing element so as toseparate the transmitted light into waveband light having itspolarization direction changed and waveband light not having itspolarization direction changed; the waveband light having itspolarization direction changed by the second polarization directionchanging element may be reflected from the second polarizationseparation element as further reflected light corresponding to one ofthe other two of the three colors; and the waveband light not having itspolarization direction changed by the second polarization directionchanging element may pass through the second polarization separationelement as further transmitted light corresponding to the other one ofthe other two of the three colors.

The color separation device of the first type according to the presentinvention may comprises a first combined optical element having thefirst polarization direction changing element adhesively provided on aninclined surface of a first optical prism and the first polarizationseparation element stacked on the first polarization direction changingelement, and a second combined optical element having the secondpolarization separation element adhesively provided on one of twoorthogonal inclined surfaces of a second optical prism and the secondpolarization direction changing element adhesively provided on the otherone of the two orthogonal inclined surfaces of the second optical prism.The first combined optical element and the second combined opticalelement are optically integrated so that the first polarizationseparation element adheres to the second polarization direction changingelement.

According to the present invention, there is provided a color separationdevice of a second type that comprises a first color separation memberhaving a color separation function element that reflects or transmitsincident light of a certain color and a polarization direction changingelement that changes polarization directions of different predeterminedwavebands of the incident light in different modes, and a second colorseparation member having a polarization separation element. Linearlypolarized light being made incident on the first color separation memberat an angle of approximately 45 degree so as to separate the linearlypolarized light into reflected light and transmitted light, bothreflected light and transmitted light having different colors and one ofthe different colors corresponding to one of three colors, and one ofthe reflected light and the transmitted light being made incident on thesecond color separation member so as to separate one of the reflectedlight and the transmitted light into further reflected light and furthertransmitted light, both further reflected light and further transmittedlight corresponding to the other two of the three colors, respectively.

In such a color separation device of the second type according to thepresent invention, the first color separation member may be provided inparallel with the polarization direction changing element.

In such a color separation device of the second type according to thepresent invention, the linearly polarized light may be made incident onthe color separation function element at an angle of approximately 45degrees so as to separate the linearly polarized light into reflectedlight and transmitted light, both reflected light and transmitted lighthaving different colors and one of the different colors corresponding toone of the three colors; one of the reflected light and the transmittedlight may pass through the polarization direction changing element so asto separate one of the reflected light and the transmitted light intowaveband light having its polarization direction changed and wavebandlight not having its polarization direction changed; the waveband lighthaving its polarization direction changed by the polarization directionchanging element may be reflected from the polarization separationelement as reflected light corresponding to one of the other two of thethree colors; and the waveband light not having its polarizationdirection changed by the polarization direction changing element maypass through the polarization direction changing element as transmittedlight corresponding to the other one of the other two of the threecolors.

In such a color separation device of the second type according to thepresent invention, the color separation function element may be providedon an inclined surface of a first optical prism; the polarizationdirection changing element may be provided on a first inclined surfaceof a second optical prism; the polarization separation element may beprovided on a second inclined surface of the second optical prism; andthe first optical prism and the second optical prism may be arranged sothat the color separation function element faces in parallel with thepolarization direction changing element.

As described above, in the color separation devices according to thepresent invention, since the polarization separation elements are usedto separate the three colors from the linearly polarized light, it ispossible to perform color separation with a higher polarization degree.

According to the present invention, there is provided an imaging opticalengine that comprises a color separation device of a first typeaccording to the present invention; a first light valve, a second lightvalve, and a third light valve, each of the light valves receiving oneof the three colors separated from the linearly polarized light by thecolor separation device and generating image light corresponding to theone of the three colors; and a color combining element combining imagesformed with each of the three colors at the first light valve, thesecond light valve, and the third light valve, respectively, so thatcolor image light can be generated.

In such an imaging optical engine according to the present invention,the first light valve, the second light valve, and the third light valvemay be reflective light valves that control polarization directions;illumination light that passes through the first polarization directionchanging element, the first polarization separation element, and thesecond polarization direction changing element, respectively, and thatis reflected by the second polarization separation element may beapplied to the first light valve, image light reflected therefrom may beseparated from the illumination light by the second polarizationseparation element so as to generate image light corresponding to afirst color; illumination light that passes through the firstpolarization direction changing element, the first polarizationseparation element, the second polarization direction changing element,and the second polarization separation element, respectively, may beapplied to the second light valve, image light reflected therefrom maybe separated from the illumination light by the second polarizationelement so as to generate image light corresponding to a second color,the image light corresponding to the first color and the image lightcorresponding to the second color may be also combined by the secondpolarization separation element; illumination light that passes throughthe first polarization direction changing element, that is reflected bythe first polarization separation element, that passes through the firstpolarization direction changing element again, and further passesthrough a third polarization separation element may be applied to thethird light valve, image light reflected therefrom may be separated fromthe illumination light by the third polarization separation element soas to generate image light corresponding to a third color; and combinedimage light corresponding to both the first color and the second colormay be further combined with the image light corresponding to the thirdcolor so that the color image light can be generated.

In the imaging optical engine according to the present invention, thefirst polarization separation element supported between the firstpolarization direction changing element and the second polarizationdirection changing element, the second polarization separation element,the third polarization separation element, and the color combiningelement may be arranged in the form a cross.

In the imaging optical engine according to the present invention, thefirst polarization separation element supported between the firstpolarization direction changing element and the second polarizationdirection changing element, the second polarization separation element,the third polarization separation element, and the color combiningelement may be arranged on orthogonal inclined surfaces of each of fourright-angle prisms, and the orthogonal inclined surfaces of each of thefour right-angle prisms may be arranged to face one another so that thefirst polarization separation element supported between the firstpolarization direction changing element and the second polarizationdirection changing element, the second polarization separation element,the third polarization separation element, and the color combiningelement are integrated in the form of a block.

In the imaging optical engine according to the present invention, athird polarization direction changing element may be provided on anoutgoing optical path of the color image light generated by the colorcombining element so as to make polarization directions of the imagelight corresponding to the first color, the second color, and the thirdcolor in the color image light coincide with one another.

Further, the third polarization direction changing element may bedetachably provided on the outgoing optical path of the color imagelight.

In the imaging optical engine according to the present invention, apolarizer may be detachably provided at the end of an outgoing opticalpath of the color image light generated by the color combining element.

In the imaging optical engine according to the present invention, apolarizer may be detachably provided on an illumination light incidentside of the imaging optical engine.

According to the present invention, there is provided an imaging opticalengine that comprises a color separation device of a second typeaccording to the present invention; a first light valve, a second lightvalve, and a third light valve, each of the light valves receiving oneof the three colors separated from the linearly polarized light by thecolor separation device and generating image light corresponding to oneof the three colors; and a color combining element combining imagesformed with each of the three colors at the first light valve, thesecond light valve, and the third light valve, respectively, so thatcolor image light can be generated.

In such an imaging optical engine according to the present invention,the first light valve, the second light valve, and the third light valvemay be reflective light valves that control polarization directions;illumination light that passes through the color separation functionelement and the polarization direction changing element, respectively,and that is reflected by the polarization separation element may beapplied to the first light valve, image light reflected therefrom may beseparated from the illumination light by the polarization separationelement so as to generate image light corresponding to a first primarylight; illumination light that passes through the color separationfunction element, the polarization direction changing element, and thepolarization separation element, respectively, may be applied to thesecond light valve, image light reflected therefrom may be separatedfrom the illumination light by the polarization separation element so asto generate image light corresponding to a second color, the image lightcorresponding to the first color and the image light corresponding tothe second color may be also combined by the polarization separationelement; illumination light that is reflected by the color separationfunction element and that passes though an additional polarizationseparation element may be applied to the third light valve, image lightreflected therefrom may be separated from the illumination light by theadditional polarization separation element so as to generate image lightcorresponding to a third color; and combined image light correspondingto both the first color and the second color may be further combinedwith the image light corresponding to the third color so that the colorimage light can be generated.

In the imaging optical engine according to the present invention, thecolor separation function element and the polarization directionchanging element configuring the first color separation member, thepolarization separation element, the additional polarization separationelement, and the color combining element may be arranged in the form ofa cross.

In the imaging optical engine according to the present invention, thecolor separation function element and the polarization directionchanging element configuring the first color separation member, thepolarization separation element, the additional polarization separationelement, and the color combining element may be arranged on orthogonalinclined surfaces of each of four right-angle prisms, and the colorseparation function element and the polarization direction changingelement configuring the first color separation member, the polarizationseparation element, the additional polarization separation element, andthe color combining element may be integrated in the form of a block.

In the imaging optical engine according to the present invention, anadditional polarization direction changing element may be provided on anoutgoing optical path of the color image light generated by the colorcombining element so as to make polarization directions of the imagelights corresponding to the first color, the second color, and the thirdcolor in the color image light coincide with one another.

Further, the additional polarization direction changing element may bedetachably provided on the outgoing optical path of the color imagelight.

In the imaging optical engine according to the present invention, apolarizer may be detachably provided at the end of an outgoing opticalpath of the color image light generated by the color combining element.

In the imaging optical engine according to the present invention, apolarizer may be detachably provided on an illumination light incidentside of the imaging optical engine.

As described above, since the color separation devices according to thepresent invention are applied to the imaging optical engines that uselight valves so as to control polarization directions, it is possible toobtain the color image (color image light) with high contrast.

In addition, in the imaging optical engines according to the presentinvention, since no polarization direction changing elements arearranged on optical paths between each of the light valves and a colorcombining part where each image light reflected from respective lightvalves are combined, it is possible to easily make the optical pathlength of each image light reflected from respective light valves andcorresponding to each of the three colors, respectively, coincide withone another.

According to the present invention, there is provided a projectionapparatus that comprises an imaging optical engine including a colorseparation device of a first type or of a second type according to thepresent invention and a projection lens. The color image lightcorresponding to the three colors is generated from the imaging opticalengine and the color image light is projected onto a screen by theobjection lens.

As described above, since the imaging optical engines according to thepresent invention are applied to the projection apparatus, it ispossible to increase image quality of color images provided from theprojection apparatus. Also, since no polarization direction changingelements that are inclined at an angle of 45 degrees are arranged on theoptical paths between each of the light valves and the color combiningpart, it is possible to prevent the reduction in the quality of thecolor images projected from the projection apparatus, thus a lesserrequirement exists for the design of the projection lens.

Therefore, according to the present invention, by suitably combining thefirst color separation member that comprises a polarization directionchanging element and a polarization separation element/color separationfunction element and the second color separation member that comprises apolarization separation element, it is possible to realize a colorseparation device that can perform color separation so that thepolarization direction of each of color components in the combined colorimage light is made coincident with one another.

Further, when such a color separation device according to the presentinvention is used, it is possible to realize an imaging optical enginethat has imaging optical path length for respective colors, whichoptical paths lie between respective light valves and the colorcombining part, made coincident with one another since the polarizationdirection changing elements are eliminated from the optical pathsbetween the respective light valves and the color combining part.

Further, when such an imaging optical engine is used, it is possible torealize a projection apparatus that can provide high quality colorimages since the color separation can be performed with a higherpolarization degree.

In addition, according to the present invention, it is possible torealize an imaging optical engine and a projection apparatus of highquality by effectively improving the contrast of the color images to beprojected on to a screen since the color separation can be performedwith a higher degree.

Further, according to the present invention, it is possible to realizean adjustable projection apparatus that can adapt to the case whenpriority is given to the brightness over the contrast of the colorimages to be projected on to a screen, according to the user's intendedpurposes since an additional polarization direction changing element maybe detachably provided on the outgoing optical path of the color imagelight.

Lastly, according to the present invention, since no inclinedpolarization direction changing elements are arranged on the opticalpath between each of the light valves and the color combining part, itis possible to realize a projection apparatus having a configurationthat prevents the quality reduction of the combined color image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration of one example of a projectionapparatus mounted on a three-panel liquid crystal projector according tothe related art;

FIG. 2 is a schematic configuration of another example of a projectionapparatus mounted on a liquid crystal projector device according to therelated art;

FIG. 3 shows a schematic configuration of a color separation deviceaccording to a first embodiment of the present invention;

FIG. 4 shows a schematic configuration of a color separation deviceaccording to a second embodiment of the present invention;

FIG. 5 shows a schematic configuration of a color separation deviceaccording to a third embodiment of the present invention;

FIG. 6 shows a schematic configuration of an imaging optical engine of aprojection apparatus according to a fourth embodiment of the presentinvention;

FIG. 7 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a fifth embodiment of the presentinvention;

FIG. 8 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a sixth embodiment of the presentinvention;

FIG. 9 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a seventh embodiment of the presentinvention;

FIG. 10 shows a schematic configuration of an imaging optical engine ina projection apparatus according to an eighth embodiment of the presentinvention;

FIG. 11 shows a schematic configuration of an imaging optical engine ina projection apparatus according to a ninth embodiment of the presentinvention;

FIG. 12 shows a configuration, which enables the switching between apolarizer and a dummy parallel plate, provided on an outgoing opticalpath of the imaging optical engine according to the fifth, the seventh,and the ninth embodiments of the present invention shown in FIG. 7, FIG.9, and FIG. 11, respectively;

FIG. 13 shows a schematic configuration of a color separation deviceaccording to a tenth embodiment of the present invention;

FIG. 14 shows a schematic configuration of a color separation deviceaccording to an eleventh embodiment of the present invention;

FIG. 15 shows a schematic configuration of a color separation deviceaccording to a twelfth embodiment of the present invention;

FIG. 16 shows a schematic configuration of an imaging optical engineaccording to a thirteenth embodiment of the present invention;

FIG. 17 shows a schematic configuration of an imaging optical engineaccording to a fourteenth embodiment of the present invention;

FIG. 18 shows a schematic configuration of an imaging optical engineaccording to a fifteenth embodiment of the present invention;

FIG. 19 shows a schematic configuration of an imaging optical engineaccording to a sixteenth embodiment of the present invention;

FIG. 20 shows a schematic configuration of an imaging optical engineaccording to a seventeenth embodiment of the present invention; and

FIG. 21 shows a schematic configuration of an imaging optical engineaccording to an eighteenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, principles and embodiments of the present inventionwill be described with reference to the accompanying drawings.

FIG. 3 shows a schematic configuration of a color separation deviceaccording to a first embodiment of the present invention. The colorseparation device according to the first embodiment is provided with afirst color separation member 100 having a first polarization separationelement supported between two wavelength selective retarders, eachwavelength selective retarder changing polarization direction ofdifferent predetermined wavelength regions of light and a second colorseparation member 104 configured from a second polarization separationelement.

In particular, the first color separation member 100 includes a firstpolarization separation element 101, a first wavelength selectiveretarder 102 and a second wavelength selective retarder 103, eachwavelength selective retarder changing the polarization direction ofdifferent predetermined wavelength regions of light. The firstpolarization separation element 101 is supported between the firstwavelength selective retarder 102 and the second wavelength selectiveretarder 103. The second color separation member 104 is configured bythe second polarization separation element 105.

Substantially linearly polarized white light is incident on the firstwavelength selective retarder 102 at an angle of approximately 45degrees. Waveband light having its polarization direction changed bypassing through the first wavelength selective retarder 102 and wavebandlight not having its polarization direction changed by passing throughthe first wavelength selective retarder 102 are separated as reflectedlight and transmitted light by the first polarization separation element101. The reflected light separated from the transmitted light passesthrough the first wavelength selective retarder 102 again and thetransmitted light, which passes through the first polarizationseparation element 101, further passes through the second wavelengthselective retarder 103, which is provided so as to face in parallel withthe first wavelength selective retarder 102. Waveband light having itspolarization direction changed by passing through the second wavelengthselective retarder 103 and waveband light not having its polarizationdirection changed by passing through the second wavelength selectiveretarder 103 are further separated as reflected light and transmittedlight, each having a different color, by the second polarizationseparation element 105.

In further detail, the color separation device shown in FIG. 3 includesa first polarization beam splitter (PBS) 100, which is configured fromthe first polarization separation element (for example, a polarizationseparation film) 101 supported between the first wavelength selectiveretarder 102, which is an element (G/M element) rotating thepolarization direction of green waveband light (G) by 90 degrees, andthe second wavelength selective retarder 103, which is an element (R/Celement) rotating the polarization direction of red waveband light (R)by 90 degrees, and a second polarization beam splitter (PBS) 104, whichis configured from the second polarization separation element (forexample, a polarization separation film) 105 supported between tworight-angle prisms 106 a, 106 b. The second PBS, i.e. the second colorseparation member 104 is arranged in the direction in which theillumination light passes through the first PBS, i.e. the first colorseparation member 100.

It is assumed that the light incident on the first PBS 100 issubstantially linearly polarized white illumination light (p-polarizedlight with respect to the first polarization separation element 101)generated from an illumination optical system (not shown). When thisp-polarized white illumination light passes through the first wavelengthselective retarder (G/M element) 102, only the green component of thelight is s-polarized and is reflected from the first polarizationseparation element 101. The reflected s-polarized green light passesthrough the first wavelength selective retarder (G/M element) 102 againand it becomes a p-polarized green light (Gp). Whereas, the p-polarizedmagenta light (M), which passes through the first polarizationseparation element 101, further passes through the second wavelengthselective retarder (R/C element) 103 and only the red component of themagenta light is s-polarized. Thus, the magenta light having thes-polarized red light component (Rs) and the p-polarized blue lightcomponent (Bp) is incident on the second PBS 104. The's-polarized redlight (Rs) is reflected from the second polarization separation element105 and the p-polarized blue light (Bp) passes through the secondpolarization separation element 105, thus the magenta light is separatedinto the s-polarized red light (Rs) and the p-polarized blue light (Bp).Accordingly, the color separation device according to the firstembodiment of the present invention shown in FIG. 3 is able to separatethe white light into three primary colors including red, blue, and greenand direct respective light corresponding to each primary color todifferent directions.

FIG. 4 shows a schematic configuration of a color separation deviceaccording to a second embodiment of the present invention. The colorseparation device according to the second embodiment includes a firstPBS 108 in the form of a prism, which includes the first polarizationseparation element (for example, a polarization separation film) 101supported between the first wavelength selective retarder 102, i.e. theelement (G/M element) rotating the polarization direction of the greenwaveband light (G) by 90 degrees and the second wavelength selectiveretarder 103, i.e. the element (R/C element) rotating the polarizationdirection of the red waveband light (R) by 90 degrees. The first PBS 108further includes two right-angle prisms 107 a, 107 b supporting thecombination of first polarization separation element 101, the firstwavelength selective retarder 102, and the second wavelength selectiveretarder 103 between them.

Other configurations, operations, and functions of the color separationdevice according to the second embodiment are similar to those of thecolor separation device according to the first embodiment of the presentinvention, therefore the descriptions of which are omitted.

The following is a description of various combinations of wavelengthselective retarders as other embodiments related to the color separationdevice shown in FIG. 3 and FIG. 4.

In the color separation devices shown in FIG. 3 and FIG. 4, thewavelength selective retarder may comprise an element (B/Y element) thatchanges the polarization direction of blue waveband light (B) by 90degrees. Therefore, if the first PBS 100 (or 108) is configured byarranging the B/Y element as the first wavelength selective retarder 102and the R/C element as the second wavelength selective retarder 103,when the p-polarized white illumination light is incident on the firstPBS 100, the blue light (B) is reflected and separated at the firstpolarization separation element 101. In the yellow light (Y) that passesthrough the first polarization separation element 101, only the redcomponent (R) of which is s-polarized by the R/C element and is incidenton the second PBS 104. The s-polarized red light (Rs) is reflected fromthe second polarization separation element 105 and the p-polarized greenlight (Gp) passes through the second polarization separation element105. Therefore, the yellow light is separated into the red light (Rs)and the green light (Gp).

Also, if the first PBS 100 (or 108) is configured by arranging the R/Celement as the first wavelength selective retarder 102 and the G/Melement as the second wavelength selective retarder 103, when thep-polarized white illumination light is incident on the first PBS 100,the red light (R) is reflected and separated at the first polarizationseparation element 101. In the cyan light (C) that passes through thefirst polarization separation element 101, only the green component (G)is s-polarized by the G/M element and is incident on the second PBS 104.The s-polarized green light (Gs) is reflected from the secondpolarization separation element 105 and the p-polarized blue light (Bp)passes through the second polarization separation element 105.Therefore, the cyan light is separated into the green light (Gs) and theblue light (Bp).

As mentioned above, since the color separation device according to thefirst and the second embodiments of the present invention includes thefirst PBS 100 (or 108) configured from the first polarization separationelement 101 supported between two different types of wavelengthselective retarders 102, 103 and the second PBS 104 configured from thesecond polarization separation element 105, it is possible to obtain theillumination light of respective primary colors in a very goodpolarization status.

FIG. 5 shows a schematic configuration of a color separation deviceaccording to a third embodiment of the present invention. The colorseparation device according to the third embodiment is configured from afirst combined optical element and a second combined optical element.The first combined optical element includes the first wavelengthselective retarder 102 adhesively provided on an inclined surface of anoptical prism 109 a and the first polarization separation element (forexample, a polarization separation film) 101 stacked on the firstwavelength selective retarder 102. The second combined optical elementincludes the second polarization separation element (for example, apolarization separation film) 105 adhesively provided on one of the twoinclined surfaces of a right-angle prism 109 b, which inclined surfacesare orthogonal to one another, and the second wavelength selectiveretarder 103 adhesively provided on the other inclined surface of theright-angle prism 109 b. The first combined optical element and thesecond combined optical element are optically integrated so that thefirst polarization separation element 101 configuring the first combinedoptical element is adhesively connected to the second wavelengthselective retarder 103 configuring the second combined optical element.

In other words, it can be said that the color separation deviceaccording to the third embodiment shown in FIG. 5 is configured suchthat the first PBS 108 and the second PBS 104 according to the secondembodiment shown in FIG. 4 are integral. Three optical prisms(right-angle prisms) 109 a, 109 b, and 109 c are used so as to arrangethe first polarization separation element 101 and the secondpolarization separation element 105 in a V-shape. The first polarizationseparation element 101 is provided between the mating surfaces of thefirst optical prism 109 a and the second optical prism 109 b and thefirst polarization separation element 101 has the first wavelengthselective retarder (for example, the G/M element) 102 and the secondwavelength selective retarder (for example, the R/C element) 103,respectively, on its both sides. In other words, the first polarizationseparation element 101 having the first wavelength selective retarder102 and the second wavelength selective retarder 103 on its both sides,respectively, is integrally supported between the first optical prism109 a and the second optical prism 109 b. The second optical prism 109 bhas the second polarization separation element 105 provided on the otherinclined surface other than the one having the second wavelengthselective retarder 103. The second polarization separation element 105is integrally supported between the second optical prism 109 b and thethird optical prism 109 c.

Other configurations, operations, and function of the color separationdevice according to the third embodiment of the present invention aresimilar to those of the color separation device according to the firstembodiment of the present invention, therefore the descriptions of whichare omitted.

FIG. 6 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a fourth embodiment of the presentinvention.

The imaging optical engine according to the fourth embodiment of thepresent invention is provided with the color separation device accordingto the first, the second, or the third embodiment of the presentinvention (in FIG. 6, the color separation device according to the firstembodiment is used). Substantially linearly polarized illumination lightis separated into three primary colors by the color separation device.The imaging optical engine according to the fourth embodiment is furtherprovided with three light valves 113, 114, and 115, each correspondingto respective separated primary colors, and a color combining element117 combining images formed with respective primary colors.

In other words, the imaging optical engine according to the fourthembodiment of the present invention is to control, with respect topixels, the polarization direction of the linearly polarized lightseparated into three primary colors, i.e. red (R), green (G), and blue(B), using the color separation device according to the first, thesecond, or the third embodiment shown in FIG. 3, FIG. 4, and FIG. 5,respectively, at the light valves for respective Primary colorsdepending on image signals. The light valves 113, 114, and 115 may betransmissive or reflective liquid crystal panels that controlpolarization directions (in FIG. 6, reflective liquid crystal panels areused). The illumination lights of a first primary color and a secondprimary color, which are separated by the second polarization separationelement 105 configuring the color separation device, are applied to thefirst light valve 113 and the second light valve 114, respectively, andthe image light reflected from respective light valves are combined bythe second polarization separation element 105 and also the image lightis separated from the illumination light by the second polarizationseparation element 105. The illumination light of a third primary color,which passes through the first wavelength selective retarder 102configuring the color separation device, which reflected from the firstpolarization separation element 101, and which passes through the firstwavelength selective retarder 102 again is applied to the third lightvalve 113 via the third polarization separation element 111. The imagelight reflected from the light valve 115 is separated from theillumination light by the third polarization separation element 111 andthus image light of the third color is generated. The two image lights,i.e. the image light with the first primary color and the second primarycolor combined together and the image light with the third color, arecombined by the color combining element 117 such as a dichroic film soas to generate the color image (color image light).

Although not shown in the figure, as for the color combining element, aso-called cross prism, in which two color combining films are arrangedin the form of a cross, that is commonly used in the conventional liquidcrystal projector, or a dichroic mirror may be used for color combining.As described above, when reflective liquid crystal panels are used aslight valves, in order to separate the illumination light and the imagelight, a separate polarization separation element may be used for therespective liquid crystal panel for optical path separation. The imagesof respective colors are combined by the color combining element such asa cross prism to obtain the color image.

In the imaging optical engine according to the fourth embodiment of thepresent invention, the color separation device according to the first,the second, or the third embodiment of the present invention is used.Since the primary colors are separated by the color separation device bythe polarization separation elements and the wavelength selectiveretarders, it is possible to perform color separation with a highpolarization degree. Therefore, when this color separation device isapplied to an imaging optical engine using transmissive or reflectiveliquid crystal panels, both of which control the polarizationdirections, it is possible to obtain color images with high contrast.Also, when such an imaging optical engine is applied to a projectionapparatus, it is possible to improve the image quality of the colorimage projected onto a screen.

In more detail, the imaging optical engine according to the fourthembodiment of the present invention shown in FIG. 6 is to separate thewhite illumination light into three primary colors, i.e. red, green, andblue, by using the color separation device configured as described inFIG. 3. This color separation device includes, for example, the firstPBS 100 having the first polarization separation element (for example, apolarization separation film) 101 supported between the first wavelengthselective retarder 102, for example, the element (G/M element) rotatingthe polarization direction of green waveband light by 90 degrees and thesecond wavelength selective retarder 103, for example, the element (R/Celement) rotating the polarization direction of red waveband light by 90degrees, all of which are arranged diagonally at an angle of 45 degrees,and the second PBS 104 having the second polarization separation element(for example, a polarization separation film) 105 supported between tworight-angle prisms 106 a, 106 b. The second PBS 104 is arranged in thedirection in which the illumination light passes through the first PBS100. The light valves 113, 114 (for example, the reflective polarizationcontrol element or reflective liquid crystal panel, etc.) for the redcomponent and for the blue component are provided on two orthogonalsurfaces of the second PBS 104, respectively, which second PBSconfigures the color separation device. Further, in the direction oflight reflected from the first PBS 100, there is arranged a third PBS110, which includes the third polarization separation element (forexample, a polarization separation film) 111 supported between tworight-angle prisms 112 a, 112 b. In the direction in which theillumination light passes through the third PBS 110, there is providedthe light valve 115 (for example, the reflective polarization controlelement and the reflective liquid crystal panels, etc.) for the greencomponent. The reflected light from the light valve 113 for the redcomponent and the light valve 114 for the blue component are combinedinto magenta light (M) by the second polarization separation element 105of the second PBS 104. At the position where the outgoing direction ofthe magenta light (M) and the outgoing direction of the green light (G),which is separated from the illumination light by being reflected fromthe third polarization separation element 111 after being reflected fromthe light valve 115 for the green component, intersect, a dichroic prism116 having the color combining element 117 (for example, a dichroicfilm) supported between two right-angle prisms 118 a, 118 b is provided.The dichroic film 117 of the dichroic prism 116 combines the magentalight (the light which combined the red image light and blue imagelight) with the green image light so as to generate the color imagelight.

It is noted that in the imaging optical engine according to the fourthembodiment of the present invention shown in FIG. 6, the firstpolarization separation element 101 supported between the firstwavelength selective retarder 102 and the second wavelength selectiveretarder 103, the second polarization separation element 105, the thirdpolarization separation element 111, and the color combining element(dichroic film) 117 are arranged in the form of a cross. In other words,since the plane surfaces including each element are arranged so as tointersect one another, it is possible to obtain a compact imagingoptical engine.

Further, when a projection apparatus is to be configured using suchimaging optical engine, an illumination optical system (not shown) maybe provided on the incident side of the imaging optical engine and aprojection lens 119 may be provided on the outgoing side of the imagingoptical engine.

The following is the description of the operation of the imaging opticalengine configured as shown in FIG. 6. It is assumed that the lightincident on the first PBS 100 is, for example, substantially linearlypolarized white illumination light (p-polarized light with respect tothe first polarization separation element 101). When this p-polarizedwhite illumination light passes through the first wavelength selectiveretarder (G/M element), only the green component of the illuminationlight is s-polarized and is reflected from the first separation element101. The reflected s-polarized green light passes through the firstwavelength selective retarder (G/M element) 102 again and it becomesp-polarized green light (Gp). Whereas the p-polarized magenta light (M:Rs+Bp), which passes through the first polarization separation element101, further passes through the second wavelength selective retarder(R/C element) 103, and only the red light component of the magenta lightis s-polarized. The magenta light having the s-polarized red lightcomponent (Rs) and the p-polarized blue light component (Bp) is incidenton the second PBS 104. The s-polarized red light (Rs) is reflected fromthe second polarization separation element 105 and the p-polarized bluelight (Bp) passes through the second polarization separation element105, thus the magenta light is separated into the s-polarized red lightand the p-polarized blue light.

As described above, after the white illumination light is separated intothree primary colors of red (R), green (G), and blue (B), the red imagelight and the blue image light reflected from the light valve 113, 114,respectively, are combined and separated from the white illuminationlight by the second polarization separation element 105 of the secondPBS 104 to generate the magenta image light (M: Rp+Bs). The magentaimage light is directed to the dichroic prism 116. Meanwhile, the greenimage light (Gs) reflected from the light valve 115 is separated fromthe illumination light by the polarization separation element 111 of thethird PBS 110 and is directed to the dichroic prism 116. The green imagelight (Gs) is combined with the magenta image light (M: Rp+Bs) by thecolor combining element (dichroic film) 117. In this combined imagelight, only the red component is p-polarized and the rest, i.e. the bluecomponent and the green component are s-polarized.

FIG. 7 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a fifth embodiment of the presentinvention. The basic configuration of the imaging optical engineaccording to the fifth embodiment is similar to that of the imagingoptical engine according to the fourth embodiment of the presentinvention shown in FIG. 6. Therefore, like reference numerals denotelike elements, the operations and functions of which are the same.

In addition to the configurations of imaging optical engine according tothe fourth embodiment of the present invention, the imaging opticalengine according to the fifth embodiment of the present invention isprovided with a third wavelength selective retarder 120, which isprovided on the outgoing optical path of the color image light, in orderto make the polarization directions of the image lights of respectiveprimary colors coincide with one another. In such case, when the thirdwavelength selective retarder 120 is an element that changes thepolarization of only the red light, the p-polarized red light componentin the color image light is s-polarized and thus the polarizationdirections of all the primary colors in the color image light arecoincided. This third wavelength selective retarder 120 is detachablyprovided on the outgoing optical path of the color image light so it canbe removed when it is not necessary.

It is noted that in the imaging optical engine configured as shown inFIG. 7, a polarizer 121 is arranged downstream of the third wavelengthselective retarder 120. For example, when the polarization directions ofthe red light, the blue light, and the green light of the color imagelight are made coincident with one another so as to be s-polarized, apolarizer that only passes through s-polarized light may be provided asthe polarizer 121 so as to cut out the undesired p-polarized componentwhich may be generated by passing through numerous optical elements andtherefore, the reduction in contrast can be effectively avoided.

Although not shown in the figure, it is also possible to provide apolarizer on the incident side of the color separation device of theimaging optical engine. In such configuration, since the polarizationcomponents of the linearly polarized light that is incident on the colorseparation device can be improved, the color purity of the colorseparation is increased.

Further, if the polarizer is to be provided on the incident side of theimaging optical engine or on the outgoing optical path of the colorimage light, it is preferable that the polarizer be detachable. Forexample, if a projection apparatus is configured using such detachablepolarizer 121 provided on the outgoing optical path of the color imagelight of the imaging optical device shown in FIG. 7, when priority isgiven to contrast, the polarizer may be provided and when priority isgiven to brightness, the polarizer may be removed as required. Further,in order to make the back focal length of the projection lens 119 equal,a dummy parallel plate, etc. may be inserted instead when the polarizer121 is removed.

In more detail, a member having the polarizer 120 and the dummy parallelplate 123 integrally formed thereon such as shown in FIG. 12 may beused. This member may be slid manually or by a driving device, etc. soas to switch between the polarizer 121 and the dummy parallel plate 123,etc. depending on user's request. The operation mechanism of the memberis not limited to sliding and it is also possible to rotate the member.Alternatively, the polarizer 121 and the dummy parallel plate 123 may befixed in a retainer such as a holder, etc., respectively, and accordingto the user's request, the holder including either the polarizer 121 orthe dummy parallel plate 123 may be removed or replaced from outside ofthe projection apparatus.

The removal of the polarizer or the replacement of the polarizer withthe dummy parallel plate as mentioned above is not limited to theprojection apparatus provided with the color separation devices usingwavelength selective retarders according to the present invention and itcan also be applied to the projection apparatus according to the relatedart in particular, in the projection apparatus using light valves of apolarization control type, the polarizer is provided on the optical pathof a projection optical system in order to improve the contrast but thebrightness is decreased by the transmission factor of the polarizer. Forexample, in a bright location, priority may be given to the brightnessrather than the contrast. When the brightness is given priority whenusing the projection apparatus that uses the light valves of thepolarization control type as mentioned above, the polarizer may bedetachably provided on the optical path of the projection optical systemand depending on the user's request, the polarizer may be removed by asimple operation in order to improve the brightness.

FIG. 8 shows a schematic configuration of an imaging optical engine in aprojection apparatus according to a sixth embodiment of the presentinvention. The imaging optical engine according to the sixth embodimentof the present invention uses a color separation device having the sameconfiguration as the second embodiment of the present invention shown inFIG. 4. Therefore, the color separation device includes the first PBS108 in the form of a prism, which PBS 108 has the first polarizationseparation element (for example, the polarization separation film) 101supported between the first wavelength selective retarder 102, which isthe element (G/M element) rotating the polarization direction of greenwaveband light by 90 degrees, and the second wavelength selectiveretarder 103, which is the element (R/C element) rotating thepolarization direction of red waveband light by 90 degrees. Thecombination of the first polarization separation element 101, the firstwavelength selective retarder 102, and the second wavelength selectiveretarder 103 is further supported between two right-angle prisms 107 a,107 b.

It is noted that configuration other than the first PBS 108, andoperations and functions of the configurations other then the first PBS108 of the imaging optical engine according to the sixth embodiment ofthe present invention are the same as the imaging optical engineaccording to the fourth embodiment of the present invention shown inFIG. 6 and therefore the descriptions of which are omitted.

FIG. 9 shows a schematic configuration of an imaging optical engine of aprojection apparatus according to a seventh embodiment of the presentinvention. The basic configuration of the imaging optical engineaccording to the seventh embodiment is the same as that of the imagingoptical engine according to the sixth embodiment of the presentinvention shown in FIG. 8. Therefore, like reference numerals aredenoted to like elements and operations of which are the same.

In addition to the configurations of the imaging optical engineaccording to the sixth embodiment of the present invention shown in FIG.8, the imaging optical engine according to the seventh embodiment of thepresent invention is provided with a third wavelength selective retarder120, which is detachably provided on the outgoing optical path of thecolor image light in order to make the polarization directions of theimage light of respective primary colors coincide with one another, andfurther a polarizer 121, which is detachably provided downstream of thethird wavelength selective retarder 120. The operations and functions ofthe third wavelength selective retarder 120 and the polarizer 121 are asdescribed in the fifth embodiment of the present invention shown in FIG.7. Also, when the polarizer is to be switched with the dummy parallelplate, the operations and the functions of such configurations are asdescribed in the fifth embodiment of the present invention shown in FIG.7.

FIG. 10 shows a schematic configuration of an imaging optical engine ofa projection apparatus according to an eighth embodiment of the presentinvention. The imaging optical engine according to the eighth embodimenthas a configuration similar to that of the imaging optical engineaccording to the fourth embodiment shown in FIG. 6. However, the firstpolarization separation element (polarization separation film) 101supported between the first wavelength selective retarder 102 and thesecond wavelength selective retarder 103, the second polarizationseparation element (polarization separation film) 105, the thirdpolarization separation element (polarization separation film) 111, andthe color combining element (dichroic film) 117 are formed on each pairof orthogonal inclined surfaces of four right-angle prisms 122 a, 122 b,122 c, and 122 d that intersect one another and the orthogonal inclinedsurfaces of each right-angle prisms 122 a, 122 b, 122 c, and 122 d thatintersect one another are arranged so as to face one another to make anintegral configuration in the form of a block. In such configuration,since respective elements arranged in the form of a cross are held byfour right-angle prisms 122 a, 122 b, 122 c, and 122 d, it is possibleto reduce the number of prisms necessary as compared to the embodimentsshown in FIG. 6 through FIG. 9 and this can effectively reduce themanufacturing cost.

It is noted that configuration, operations, and functions of the firstpolarization separation element (polarization separation film) 101, thefirst wavelength selective retarder 102, the second wavelength selectiveretarder 103, the second polarization separation element (polarizationseparation film) 105, the third polarization separation element(polarization separation film) 111, the color combining element(dichroic film) 117, and the light valves, for respective colors 113,114, and 115 are the same as that of the imaging optical engineaccording to the fourth embodiment of the present invention shown inFIG. 6 and therefore the descriptions of which are omitted.

FIG. 11 shows a schematic configuration of an imaging optical engine ofa projection apparatus according to a ninth embodiment of the presentinvention. The basic configuration of the imaging optical engineaccording to the ninth embodiment of the present invention is similar tothat of the imaging optical engine according to the eighth embodiment ofthe present invention. Therefore, like reference numerals are denoted tolike elements, and operations of which are the same.

In addition to the configuration of the imaging optical engine accordingto the eighth embodiment of the present invention shown in FIG. 10, theimaging optical engine according to the ninth embodiment is providedwith a third wavelength selective retarder 120, which is detachablyprovided on the outgoing optical path of the color image light in orderto make the polarization directions of the image light of respectivecolors coincide with one another, and further a polarizer 121, which isdetachably provided downstream of the third wavelength selectiveretarder 120. The operations and functions of the third wavelengthselective retarder 120 and the polarizer 121 are as described in thefifth embodiment of the present invention shown in FIG. 7. Also, whenthe polarizer is to be switched with the dummy parallel plate, theoperation and the function of such a configuration are as described inthe fifth embodiment of the present invention shown in FIG. 7.

In the imaging optical engine according to the various embodiments ofthe present invention shown in FIG. 6 through FIG. 11, the descriptionsare given using the G/M element as the first wavelength selectiveretarder 102 and the R/C element as the second wavelength selectiveretarder 103. However, as mentioned in the first embodiment according tothe present invention, it is apparent that various other wavelengthselective retarders may be combined and used in order to perform colorseparation.

FIG. 13 shows a schematic configuration of a color separation deviceaccording to a tenth embodiment of the present invention.

The color separation device according to the tenth embodiment of thepresent invention is provided with a first color separation member 200,which has a wavelength selective retarder that change polarizationdirections of different predetermined wavelength regions of lightprovided in parallel with a color separation function element that onlyreflects or transmits light of a certain color, and a second colorseparation member 203 configured from a polarization separation element.

In particular, the first color separation member 200 includes the colorseparation function element 201 that only reflects or transmits light ofa certain color and the wavelength selective retarder 202 that changesthe polarization direction of different predetermined wavelength regionsof light, and the color separation function element 201 and thewavelength selective retarder 202 are provided in parallel with oneanother. The second color separation member 203 includes thepolarization separation element 204.

Substantially linearly polarized light is incident on the colorseparation-function element 201 at an angle of approximately 45 degreesso that reflected light and transmitted light of different colors areseparated. One of the separated lights, i.e. the transmitted light,passes through the wavelength selective retarder 202 so as to obtain thelight having waveband light having its polarization direction changedand waveband light not having its polarization direction changed ofdifferent colors. When incident on the polarization separation element204, such light is further separated into reflected light andtransmitted light.

In further detail, the color separation device shown in FIG. 13 includesthe first color separation member 200 having the color separationfunction element (for example, a dichroic separation film) 201 thatonly, for example, reflects green waveband light (G) and the wavelengthselective retarder 202, provided in parallel with the color separationfunction element 201, that rotates the polarization direction of redwaveband light (R) by 90 degrees but does not change the polarizationdirection of cyan which is a complementary color of red, and the secondcolor separation member (PBS) 203 having the polarization separationelement (for example, the polarization separation film) 204 supportedbetween two right-angle prisms 205 a, 205 b. The second color separationmember 203 is arranged in the direction in which the light passesthrough the first color separation member 200.

It is assumed that the light incident on the first color separationmember 200 is substantially linearly polarized white illumination light(for example, p-polarized light with respect to the polarizationseparation function element 201) generated from an illumination opticalsystem (not shown). This p-polarized white illumination light isincident on the color separation function element (for example, thedichroic separation film) 201 at an angle of approximately 45 degrees.The color separation function element 201 separates the p-polarizedgreen light (Gp), as reflected light, from the illumination light bybending the optical path of the green light by 90 degrees. Meanwhile,the p-polarized magenta light (M), which passes through the colorseparation function element 201, further passes through the wavelengthselective retarder (R/C element) 202 and only the red light component ofthe magenta light is s-polarized. The magenta light having ans-polarized red light component (Rs) and a p-polarized blue lightcomponent (Bp) is incident on the second color separation member 203,which is a PBS, and the s-polarized red light (Rs) is reflected from thepolarization separation element 204 and the p-polarized blue light (Bp)passes through the polarization separation element 204. Thus, themagenta light is separated into the s-polarized red light and thep-polarized blue light. Accordingly, in the color separation deviceshown in FIG. 13, the white light can be separated into three primarycolors, i.e. green, blue, and red, and each light corresponding torespective primary colors can be directed to different directions.

FIG. 14 shows a schematic configuration of a color separation deviceaccording to an eleventh embodiment of the present invention. The colorseparation device according to the eleventh embodiment includes a firstcolor separation member 206 having the color separation function element(for example, a dichroic separation film) 201 that reflects, forexample, the green light (Gp) by bending its optical path by 90 degreesand passes through magenta light (M) and the wavelength selectiveretarder 202, i.e. the element (R/C element) provided in parallel withthe color separation function element 201, which element rotates thepolarization direction of red waveband light by 90 degrees but does notchange the polarization direction of cyan light which is thecomplementary color of red. The color separation function element 201and the wavelength selective retarder 202 are supported between tworight-angle prisms 207 a, 207 b.

Other configurations, operations, and functions of the eleventhembodiment of the present invention are similar to those of the colorseparation device according to the tenth embodiment of the presentinvention shown in FIG. 13, therefore descriptions of which are omitted.

The following is a description of various examples of a combination ofthe color separation function element 201 and the wavelength selectiveretarder 202.

In the above descriptions of the color separation device according tothe tenth and the eleventh embodiments of the present invention, thecolor separation function element is described as an element reflectingthe green waveband light but an element reflecting only the bluewaveband light or an element reflecting only the red waveband light mayalso be used.

As for the wavelength selective retarder 202, an element changing thepolarization direction of the blue waveband light by 90 degrees (B/Yelement) or an element changing the polarization direction of the greenwaveband light by 90 degrees (G/M element), etc. may be used in additionto the R/C element. Any element can be selected for the color separationfunction element 201 as long as the light passing through the colorseparation function element 201 includes two primary colors out of threeprimary colors of R, G, and B and for the wavelength selective retarder202 as long as the polarization direction of one of the two primarycolors is changed.

Also it is possible to provide the wavelength selective retarder 202 infront of the color separation function element 201 so as to make thewhite illumination light pass through the wavelength selective retarder202 first and then pass through or reflect from the color separationfunction element 201. In such configurations, the light reflected fromthe color separation function element is to pass through the wavelengthselective retarder again.

As described above, since the color separation device according to theeleventh embodiment of the present invention includes the first colorseparation member 200 having the color separation function element 201provided in parallel with the wavelength selective retarder 202, and thesecond color separation member (PBS) 203 configured from thepolarization separation element 204, it is possible to obtainillumination light of respective primary colors having a goodpolarization status.

FIG. 15 shows a schematic configuration of color separation deviceaccording to a twelfth embodiment of the present invention. In the colorseparation device according to the twelfth embodiment of the presentinvention, the wavelength selective retarder 202 is provided on a firstinclined surface of an optical prism 208 b, the color separation device204 is provided on a second inclined surface of the optical prism 208 b,and the color separation function element 201 is provided on an inclinedsurface of another optical prism 208 a. The optical prism 208 a, 208 bare arranged so that the color separation function element 201 and thewavelength selective retarder 202 face one another.

In other words, the color separation device in FIG. 15 has aconfiguration similar to that of color separation device according tothe eleventh embodiment of the present invention shown in FIG. 14.However, the first color separation member 206 and the second colorseparation member (PBS) 203 are configured so as to be integral. Threeoptical prisms (right-angle prisms) 208 a, 208 b, and 208 c are used soas to keep the color separation function element 201 supported facingthe wavelength selective retarder 202 and the polarization separationelement 204 in a V-shape. In more detail, the color separation functionelement 201 is arranged between the mating surfaces of the opticalprisms 208 a, 208 b, the wavelength selective retarder (for example, theR/C element) 202 is adhesively arranged next to the color separationfunction element 201, and thus the color separation function element 201and the wavelength selective retarder 202 are integrally arrangedbetween the optical prism 208 a and the optical prism 208 b. Thepolarization separation element 204 is arranged between the secondinclined surface of the optical prism 208 b and an inclined surface ofanother optical prism 208 c.

It is noted that element configuration, operations, and functions of thecolor separation device according to the twelfth embodiment of thepresent invention shown in FIG. 15 are as described in the colorseparation device according to the first embodiment of the presentinvention shown in FIG. 3, therefore the descriptions of which areomitted.

FIG. 16 shows a schematic configuration of an imaging optical engineaccording to a thirteenth embodiment of the present invention.

The imaging optical engine according to the thirteenth embodiment isprovided with the color separation device according to the tenth, theeleventh, or the twelfth embodiment (in FIG. 16, the color separationdevice according to the tenth embodiment is used). Substantiallylinearly polarized illumination light is separated into three primarycolors by the color separation device. The imaging optical engineaccording to the thirteenth embodiment further includes three lightvalves 212, 213, and 214, each corresponding to respective separatedprimary colors, and a color combining element 215 for combining eachcolor image formed by the respective light valves.

In other words, the imaging optical engine according to the thirteenthembodiment of the present invention is to control, with respect topixels, the polarization direction of the linearly polarized lightseparated into three primary colors, i.e. red (R), green (G), and blue(B) using the color separation device according to the tenth, theeleventh, or the twelfth embodiment of the present invention shown inFIG. 13, FIG. 14, and FIG. 15, respectively, at the light valves forrespective primary colors depending on the image signals. The lightvalves 212, 213, and 214 may be transmissive or reflective liquidcrystal panels that control polarization directions (in FIG. 16,reflective liquid crystal panels are used). The illumination lights ofthe first primary color and the second primary color, which areseparated by the polarization separation element 204 of the second PBS203 configuring the color separation device, are applied to the firstlight valve 212 and the second light valve 213, respectively, and theimage light reflected from respective light valves are combined by thepolarization separation element 204 and also the image light isseparated from the illumination light by the polarization separationelement 204. The illumination light of the third primary color separatedby the color separation function element 201 configuring the first colorseparation member 200 of the color separation device is applied to thethird light valve 214 via the second polarization separation element 210and the image light reflected from the light valve 214 is separated fromthe illumination light by the second polarization separation element 210and thus image light of the third color is generated. Two image lights,i.e. the image light with the first primary color and the second primarycolor combined together and the image light with the third color, arecombined by the color combining element 216 and the color image (colorimage light) is generated.

Although not shown in the figure, as for the color combining element, aso-called cross prism, in which two color combining films are arrangedin the form of a cross, that is commonly used in the liquid crystalprojector according to the related art or a dichroic mirror may be usedto combine primary colors. As described above, when reflective liquidcrystal panels are used as light valves, in order to separate theillumination light and the image light, a separate polarizationseparation element may be used for the respective liquid crystal panelfor optical path separation. The images of respective colors arecombined by the color combining element such as a cross prism to obtainthe color image.

In the imaging optical engine according to the thirteenth embodiment ofthe present invention, the color separation device according to thetenth, the eleventh, or the twelfth embodiment of the present inventionis used. Since the primary colors are separated by the color separationdevice using the color separation function element, the wavelengthselective retarder, and the polarization separation element, it ispossible to perform color separation with a high polarization degree.Therefore, when this color separation device is applied to an imagingoptical engine using transmissive or reflective liquid crystal panels,both of which control the polarization directions, it is possible toobtain color images with high contrast. Also, when such an imagingoptical engine is applied to a projection apparatus, it is possible toimprove the image quality of the color image projected onto a screen.

In more detail, the imaging optical engine according to the thirteenthembodiment shown in FIG. 16 is to separate the white illumination lightinto three primary colors, i.e. red, green, and blue, by using the colorseparation device configured as described in FIG. 13. This colorseparation device includes the first color separation member 200 and thesecond color separation member (PBS) 203. The first color separationmember 200 includes the color separation function element (for example,a dichroic separation film) 201 that only reflects the green wavebandlight and the wavelength selective retarder 202, i.e. the element (R/Celement) provided in parallel with the color separation function element201, which R/C element rotates the polarization direction of the redwaveband light by 90 degrees. The second color separation member 203includes the polarization separation element 204 supported between tworight-angle prisms 205 a, 205 b. The second color separation member(PBS) 203 is arranged in the direction in which the illumination lightpasses through the first color separation member 200. The light valves212, 213 (for example, reflective polarization control elements orreflective liquid crystal panels, etc.) for the red light (R) and forthe blue light (b) are provided on two orthogonal surfaces of the secondcolor separation member (PBS) 203, respectively. Further, in thedirection of light reflected from the color separation function element(for example, a dichroic separation film) 201 of the first colorseparation member 200, there is arranged a second PBS 209 having asecond polarization separation element (for example, a polarizationseparation film) 210 supported between two right-angle prisms 211 a, 211b. In the direction in which the illumination light passes through thesecond PBS 209, there is provided the light valve 214 (for example, areflective polarization control element or a reflective liquid crystalpanel, etc.) for green light (G). The reflected light from the lightvalve 212 for the red light (R) and the light valve 213 for the bluelight (B) are combined into magenta light (M) by the polarizationseparation element 204 of the second color separation member (PBS) 203.At the position where the outgoing direction of the magenta light andthe outgoing direction of the green light, which is separated from theillumination by reflecting from the second polarization separationelement 210 after reflected from the light valve 214 for the green light(G), intersect, the dichroic prism 215 having the color combiningelement (a dichroic film) 216 supported between two right-angle prisms217 a, 217 b is provided. This dichroic film 216 of the dichroic prism215 combines the magenta light (the light which combined the red lightand the blue light) with the green light as to generate and output colorimage light.

It is noted that in the imaging optical engine according to thethirteenth embodiment shown in FIG. 16, the color separation functionelement 201 and the wavelength selective retarder 202, both configuringthe color separation device, the polarization separation element 204,the second polarization separation element 210, and the color combiningelement (dichroic film) 216 are arranged in the form of a cross. Inother words, since the plane surfaces including each element arearranged so as to intersect one another, it is possible to obtain acompact imaging optical engine.

Further, when a projection apparatus is to be configured using such animaging optical engine, an illumination optical system (not shown) maybe provided on the incident side of the imaging optical engine and aprojection lens 218 may be provided on the outgoing direction of thecolor image light combined at the dichroic prism 215.

The following is the description of an operation of the imaging opticalengine configured as shown in FIG. 16. It is assumed that the lightincident on the first color separation member 200 is, for example,substantially linearly polarized white illumination light (p-polarizedlight with respect to the polarization separation element 204) generatedfrom an illumination optical system (not shown). This p-polarized whiteillumination light is incident on the color separation function element(for example, a dichroic separation film) 201 at an angle of 45 degrees.The color separation function element 201 separates the p-polarizedgreen light (Gp) as reflected light from the illumination light bybending the optical path of the green light by 90 degrees. Meanwhile,the p-polarized magenta light (M: Rs+Bp), which passes through the colorseparation function element 201, further passes through wavelengthselective retarder (R/C element) 202 and only the red light component ofthe magenta light is s-polarized. Thus the magenta light having thes-polarized red light component (Rs) and the p-polarized blue lightcomponent (Bp) are incident on the second color separation member 203,which is a PBS, and the s-polarized red light (Rs) is reflected from thepolarization separation element 204 and the p-polarized blue light (Bp)passes through the polarization separation element 204. Thus, themagenta light is separated into the s-polarized red light and thep-polarized blue light.

As described above, after the white illumination light is separated intothree primary colors of red (R), blue (B), and green (G), the red imagelight and the blue image light reflected from the light valve 212, 213,respectively, are combined and separated from the white illuminationlight by the polarization separation element 204 of the second colorseparation member (i.e. PBS) 203 to generate the magenta image light (M:Rs+Bp). The magenta image light is directed to the dichroic prism 215.Meanwhile, the green image light (Gs) reflected from the light valve 214is separated from the illumination light by the polarization separationelement 210 of the second PBS 209 and is directed to the dichroic prism215. The green image light (Gs) is combined with the magenta image lightby the color combining element (dichroic film) 216. In this combinedimage light, only the red component is p-polarized and the rest, i.e.the blue component and the green component, are s-polarized.

FIG. 17 shows a schematic configuration of an imaging optical engine ina projection apparatus according to a fourteenth embodiment of thepresent invention. The basic configuration of the imaging optical engineaccording to the fourteenth embodiment is similar to that of the imagingoptical engine according the thirteenth embodiment shown in FIG. 16.Therefore, like reference numerals are denoted to like elements, andoperations and functions of which are the same.

In addition to the configurations of the imaging optical engineaccording to the thirteenth embodiment shown in FIG. 16, the imagingoptical engine according to the fourteenth embodiment of the presentinvention is provided with a second wavelength selective retarder 219,which is provided on the outgoing optical path of the color image lightin order to make the polarization directions of the image light ofrespective primary colors coincide with one another. In such case, whenthe second wavelength selective retarder 219 is an element that changesthe polarization direction of only the red light, the p-polarized redlight component in the color image light is s-polarized and thus thepolarization direction of the image light of respective primary colorscan be coincident. This second wavelength selective retarder 219 isdetachably provided on the outgoing optical path of the color imagelight, so it can be removed when it is not necessary.

It is noted that in the imaging optical engine configured as shown inFIG. 17, a polarizer 220 is arranged downstream of the second wavelengthselective retarder 219. For example, when the polarization directions ofthe red light, the blue light, and the green light of the color imagelight are made coincident with one another so as to be s-polarizedlight, a polarizer that only passes through s-polarized light may beprovided as the polarizer 220 so as to cut out the undesired p-polarizedcomponent which may be generated by passing through numerous opticalelements. Therefore, the reduction in contrast can be effectivelyavoided.

Although not shown in the figure, it is also possible to provide apolarizer on the incident side of the color separation device of theimaging optical engine. In such a configuration, since the polarizationcomponents of the linearly polarized light that is incident on the colorseparation device can be improved, the color purity of the colorseparation is increased.

Further, if the polarizer is to be arranged on the incident side of theimaging optical engine or on the outgoing optical path of the colorimage light, it is preferable that the polarizer be detachable. Forexample, if a projection apparatus is configured using such detachablepolarizer 220 provided on the outgoing optical path of the color imagelight of the imaging optical device shown in FIG. 17, when priority isgiven to the contrast, the polarizer may be provided and when priorityis given to the brightness, the polarizer may be removed as required.Further, in order to make the back focal length of the projection lens218 equal, a dummy parallel plate, etc. may be inserted instead when thepolarizer 220 is removed.

In more detail, as for the configuration that enables the switchingbetween the polarizer and the dummy parallel plate, the configurationshown in FIG. 12, which configuration is described according to thefifth embodiment of the present invention, may be used. In particular, amember having the polarizer and the dummy parallel plate integrallyformed thereon as shown in FIG. 12 is provided and this member may beslid manually or by a driving device, etc. so as to switch between thepolarizer and the dummy parallel plate, etc. depending on the user'srequest. The operation mechanism of the member is not limited to slidingbut it is also possible to rotate the member. Alternatively, thepolarizer and the dummy parallel plate may be fixed in a retainer suchas a holder, etc., respectively, and according to the user's request,the holder including either the polarizer or the dummy parallel platemay be removed or replaced from outside of the projection apparatus.

FIG. 18 shows a schematic configuration of an imaging optical engine ofa projection apparatus according to a fifteenth embodiment of thepresent invention. The imaging optical engine according to the fifteenthembodiment uses the color separation device having the sameconfigurations as that of the color separation device according to theeleventh embodiment of the present invention shown in FIG. 14. Thiscolor Separation device includes the first color separation functionelement 206 having the color separation function element (for example, adichroic separation film) 201 that reflects, for example, the greenlight by bending its optical path by 90 degrees and passes through themagenta light and the wavelength selective retarder 202, i.e. theelement (R/C element) provided in parallel with the color separationfunction element 201, which R/C element rotates the polarizationdirection of red waveband light by 90, degrees and which does not changethe polarization direction of cyan light that is the complementary colorof red. The color separation function element 201 and the wavelengthselective retarder 202 are supported between two right-angle prisms 207a, 207 b.

Configuration, operations, and functions of the fifteenth embodiment ofthe present invention other than the first color separation member 206in the form of a prism are similar to those of the imaging opticalengine according to the thirteenth embodiment shown in FIG. 16,therefore descriptions of which are omitted.

FIG. 19 shows a schematic configuration of an imaging optical engine ofa projection apparatus according to a sixteenth embodiment of thepresent invention. The basic configuration of the imaging optical engineaccording to the sixteenth embodiment is similar to that of the imagingoptical engine according to the fifteenth embodiment of the presentinvention shown in FIG. 18, therefore, like reference numerals aredenoted to like elements and operations of which are the same.

In addition to the configurations of the imaging optical engineaccording to the fifteenth embodiment of the present invention shown inFIG. 18, the imaging optical engine according to the sixteenthembodiment of the present invention is provided with a second wavelengthselective retarder 219, which is detachably provided on the outgoingoptical path of the color image light in order to make the polarizationdirections of the image light of respective primary colors coincide withone another, and further a polarizer 220, which is detachably provideddownstream of the second wavelength selective retarder 219. Theoperations and functions of the second wavelength selective retarder 219and the polarizer 220 are as described in the fourteenth embodiment ofthe present invention shown in FIG. 17. Also, when the polarizer is tobe switched with the dummy parallel plate, the operations and thefunctions of such configurations are as described in the fourteenthembodiment of the present invention shown in FIG. 17.

FIG. 20 shows a schematic configuration of an imaging optical engine ina projection apparatus according to a seventeenth embodiment of thepresent invention. The imaging optical engine according to theeighteenth embodiment has a configuration similar to that of the imagingoptical engine according to the thirteenth embodiment of the presentinvention shown in FIG. 16. However, the color separation functionelement 201 and wavelength selective retarder 202, both configuring thecolor separation device, the polarization separation element 204, thesecond polarization separation element 210, and the color combiningelement (dichroic film) 216 are provided on each pair of orthogonalinclined surfaces of four right-angle prisms 221 a, 221 b, 221 c, and221 d that intersect one another and the orthogonal inclined surfaces ofeach right-angle prisms 221 a, 221 b, 221 c, and 221 d that intersectone another are arranged so as to face one another to make an integralconfigurations in the form of a block. In such a configuration, sincerespective elements arranged in the form of a cross are held by fourright-angle prisms 221 a, 221 b, 221 c, and 221 d, it is possible toreduce the number of prisms necessary as compared to the embodimentsshown in FIG. 16 through FIG. 19 and this can effectively reduce themanufacturing cost.

It is noted that configuration, operations, and functions of the colorseparation function element (dichroic separation film) 201 and thewavelength selective retarder 202, both configuring the color separationdevice, the polarization separation element (polarization separationfilm) 204, the second polarization separation element (polarizationseparation film) 210, the color combining element (dichroic film) 216,and the light valves 212, 213, and 214 for respective colors are asdescribed in the thirteenth embodiment of the present invention shown inFIG. 16 and therefore, the descriptions of which are omitted.

FIG. 21 shows a schematic configuration of an imaging optical engine ofa projection apparatus according to an eighteenth embodiment of thepresent invention. The basic configuration of the imaging optical engineaccording to the eighteenth embodiment is similar to that of the imagingoptical engine according to the seventeenth embodiment shown in FIG. 20.Therefore, like reference numerals are denoted to like elements, andoperations of which are the same.

In addition to the configuration of the imaging optical engine accordingto the seventeenth embodiment shown in FIG. 20, the imaging opticalengine according to the eighteenth embodiment of the present inventionis provided with a second wavelength selective retarder 219, which isdetachably provided on the outgoing optical path of the color imagelight in order to make the polarization directions of the image light ofrespective primary colors coincide with one another, and further apolarizer 220, which is detachably provided downstream of the secondwavelength selective retarder 219. The operations and functions of thesecond wavelength selective retarder 219 and the polarizer 220 are asdescribed in the fourteenth embodiment of the present invention shown inFIG. 17. Also, when the polarizer is to be switched with the dummyparallel plate, the operations and the functions of such configurationsare as described in the fourteenth embodiment of the present inventionshown in FIG. 17.

In the above descriptions of the imaging optical engines according tothe thirteenth to the eighteenth embodiment of the present invention,the color separation function element 201 is described as a green lightreflective dichroic separation film and the wavelength selectiveretarder 202 as a R/C element but it is apparent that any one of variouscombinations of a color separation function element and a wavelengthselective retarder may be used in order to perform color separation asmentioned in the tenth embodiment of the present invention.

The following is a detailed description of embodiments according to thepresent invention where one of the imaging optical engines describedabove is applied to a projection apparatus. The configuration of theimaging optical engine is one of the configurations shown in FIG. 6through FIG. 11, or FIG. 16 through FIG. 21. The projection apparatus isconfigured by providing an illumination optical system on theillumination light incident side of the imaging optical engine and aprojection lens 119 or 218 on the outgoing side of the color imagelight. The illumination optical systems are omitted in FIG. 6 throughFIG. 11 and FIG. 16 through FIG. 21.

The illumination optical system may be formed from a light source and acondenser element for illumination (illumination lens) that collimateslight flux uniformly, etc. A halogen lamp, a xenon lamp, a metal halidelamp, and a very-high-pressure mercury lamp, etc. may be used as thelight source. Also, in order to obtain good illuminance, a reflector maybe provided to reflect and collect emanated light from the light source.

In order to obtain linearly polarized light in one direction as theillumination light, a polarization changer, which is configured bycombining a PBS array and a wavelength plate and used conventionally,may be used. A linear polarizer may be inserted downstream of thepolarization changer in the illumination optical system when improvementin the polarization degree and assurance in contrast performance arerequired. Further, it is effective when the polarization degree isimproved by using the PBS. When the linear polarizer is used, heat maybe generated by light absorption and thus the performance may bedecreased but when the PBS is used, unwanted polarization components maybe reflected or transmitted and thus it is possible to better suppressthe generation of heat due to the light absorption. Therefore, it can besaid that the PBS is more effective. In particular, the PBS of a platetype so-called a wire-grid polarizer described in U.S. Pat. No.6,234,634 may be used. Obviously, this type of polarizer may be providednot only on the side of the illumination lens but also on the side ofthe projection lens. Further, the wire-grid polarizer may be used as thepolarization separation element, which is a configuration requirement ofthe present invention.

The illumination condenser element (illumination lens) as an opticalsystem for effectively illuminating the light valves (reflective liquidcrystal panels, etc.) may beta condenser element, which is a combinationof a fly-eye lens called the integrator and which decreases theunevenness in the illuminance applied to the light valves, or thecondenser element which is combined with the condenser lens so as toguide the light effectively to the light valves. Further, aconfiguration combining the lens array corresponding to the PBS arraypitches may be used when necessary in order to improve the uniformity ofthe illuminance distribution over the illuminated area. When a lightsource having a higher polarization degree, such as a laser light sourcewith high output, etc. can be used, the polarization changer may not benecessary.

Further, the present invention is not limited to these embodiments, andvariations and modifications may be made without departing from thescope of the present invention.

The present application is based on Japanese priority application No.2001-401496 filed on Dec. 28, 2001 and Japanese priority application No.2002-053661 filed on Feb. 28, 2002, the entire contents of which arehereby incorporated by reference.

1. A method of imaging, said method comprising the steps of: a1) makinglinearly polarized light first incident on a first color separationmember of a color separation device at an angle of approximately 45degrees so as to separate the linearly polarized light into reflectedlight and transmitted light, both reflected light and transmitted lighthaving different colors and one of the different colors corresponding toone of three colors; a2) making one of the reflected light and thetransmitted light incident on a second color separation member of saidcolor separation device so as to separate said one of the reflectedlight and the transmitted light into further reflected light and furthertransmitted light, both further reflected light and further transmittedlight corresponding to the other two of the three colors, respectively;b1) receiving by a first light valve, a second light valve, and a thirdlight valve, respectively, one of the three colors separated from thelinearly polarized light by said color separation device; b2) generatingby said first light valve, said second light valve, and said third lightvalve, respectively, image light corresponding to said one of the threecolors; and c) combining by a color combining element the image lightsformed with each of the three colors at said first light valve, saidsecond light valve, and said third light valve, respectively, so thatcolor image light can be generated, wherein, said first color separationmember has a first polarization direction changing element, a secondpolarization direction changing element, each of said polarizationdirection changing element changing polarization directions of differentpredetermined wavebands of incident light in different modes, and afirst polarization separation element that reflects or transmits theincident light according to the polarization directions of the incidentlight, said second color separation member has a second polarizationseparation element, and said first polarization separation element issupported between said first polarization direction changing element andsaid second polarization direction changing element.
 2. The method ofimaging as claimed in claim 1, said method further comprising the stepsof: d1) applying to said first light valve illumination light thatpasses through said first polarization direction changing element, saidfirst polarization separation element, and said second polarizationdirection changing element, respectively, and that is reflected by saidsecond polarization separation element, and image light reflected fromsaid first light valve is separated from the illumination light by saidsecond polarization separation element so as to generate image lightcorresponding to a first color; d2) applying to said second light valveillumination light that passes through said first polarization directionchanging element, said first polarization separation element, saidsecond polarization direction changing element, and said secondpolarization separation element, respectively, and image light reflectedfrom said second light valve is separated from the illumination light bysaid second polarization element so as to generate image lightcorresponding to a second color, the image light corresponding to thefirst color and the image light corresponding to the second color arealso combined by said second polarization separation element; d3)applying to said third light valve illumination light that passesthrough said first polarization direction changing element, that isreflected by said first polarization separation element, that passesthrough said first polarization direction changing element again, andfurther passes through a third polarization separation element, andimage light reflected from said third light valve is separated from theillumination light by said third polarization separation element so asto generate image light corresponding to a third color; and e) furthercombining combined image light corresponding to both the first color andthe second color with the image light corresponding to the third colorso that the color image light can be generated, wherein, said firstlight valve, said second light valve, and said third light valve arereflective light valves that control polarization directions.
 3. Themethod as claimed in claim 2, wherein, said first polarizationseparation element, said second polarization separation element, saidthird polarization separation element, and said color combining elementare arranged in the form of a cross.
 4. The method as claimed in claim2, wherein, said first polarization separation element, said secondpolarization separation element, said third polarization separationelement and said color combining element are arranged on orthogonalinclined surfaces of each of four right-angle prisms; and the orthogonalinclined surfaces of each of the four right-angle prisms are arranged toface one another so that said first polarization separation element,said second polarization separation element, said third polarizationseparation element, and said color combining element are integrated inthe form of a block.
 5. The method of imaging as claimed in claim 1,wherein, a third polarization direction changing element is provided onan outgoing optical path of the color image light generated by saidcolor combining element so as to make polarization directions of theimage lights corresponding to the first color, the second color, and thethird color in the color image light coincide with one another.
 6. Amethod of imaging, said method comprising the steps of: a1) makinglinearly polarized light first incident on a first color separationmember of a color separation device at an angle of approximately 45degrees so as to separate the linearly polarized light into reflectedlight and transmitted light, both reflected, light and transmitted lighthaving different colors and one of the different colors corresponding toone of three colors; a2) making one of the reflected light and thetransmitted light incident on a second color separation member of saidcolor separation device so as to separate said one of the reflectedlight and the transmitted light into further reflected light and furthertransmitted light, both further reflected light and further transmittedlight corresponding to the other two of the three colors, respectively;b1) receiving by a first light valve, a second light valve, and a thirdlight valve, respectively, one of the three colors separated from thelinearly polarized light by said color separation device; b2) generatingby said first light valve, said second light valve, and said third lightvalve, respectively, image light corresponding to said one of the threecolors; and c) combining by a color combining element the image lightsformed with each of the three colors at said first light valve, saidsecond light valve, and said third light valve, respectively, so thatcolor image light can be generated, wherein, said first color separationmember has a first polarization direction changing element, a secondpolarization direction changing element, each of said polarizationdirection changing element changing polarization directions of differentpredetermined wavebands of incident light in different modes, and afirst polarization separation element that reflects or transmits theincident light according to the polarization directions of the incidentlight, said second color separation member has a second polarizationseparation element, said first polarization separation element issupported between said first polarization direction changing element andsaid second polarization direction changing element, and a polarizer isdetachably provided at the end of an outgoing optical path of the colorimage light generated by said color combining element.
 7. A method ofimaging, said method comprising the steps of: a1) making linearlypolarized light first incident on a first color separation member of acolor separation device at an angle of approximately 45 degrees so as toseparate the linearly polarized light into reflected light andtransmitted light, both reflected light and transmitted light havingdifferent colors and one of the different colors corresponding to one ofthree colors; a2) making one of the reflected light and the transmittedlight incident on a second color separation member of said colorseparation device so as to separate said one of the reflected light andthe transmitted light into further reflected light and furthertransmitted light, both further reflected light and further transmittedlight corresponding to the other two of the three colors, respectively;b1) receiving device by a first light valve, a second light valve, and athird light valve, respectively, one of the three colors separated fromthe linearly polarized light by said color separation; b2) generatingdevice by said first light valve, said second light valve, and saidthird light valve, respectively, image light corresponding to said oneof the three colors; and c) combining by a color combining element imagelights formed with each of the three colors at said first light valve,said second light valve, and said third light valve, respectively, sothat color image light can be generated, wherein, said first colorseparation member has a color separation function element that reflectsor transmits incident light of a certain color and a polarizationdirection changing element that changes polarization directions ofdifferent predetermined wavebands of the incident light in differentmodes, said second color separation member has a polarization separationelement, said color separation function element is provided on aninclined surface of a first optical prism, said polarization directionchanging element is provided on a first inclined surface of a secondoptical prism, said polarization separation element is provided on asecond inclined surface of the second optical prism, and said firstoptical prism and said second optical prism are arranged so that saidcolor separation function element faces in parallel with saidpolarization direction changing element.
 8. The method of imaging asclaimed in claim 7, said method further comprising the steps of: d1)applying to said first light valve illumination light that passesthrough said color separation function element and said polarizationdirection changing element, respectively, and that is reflected by saidpolarization separation element, and image light reflected from saidfirst light valve is separated from the illumination light by saidpolarization separation element so as to generate image lightcorresponding to a first primary light; d2) applying to said secondlight valve illumination light that passes through said color separationfunction element, said polarization direction changing element, and saidpolarization separation element, respectively, and image light reflectedfrom said second light valve is separated from the illumination light bysaid polarization separation element so as to generate image lightcorresponding to a second color, the image light corresponding to thefirst color and the image light corresponding to the second color arealso combined by said polarization separation element; d3) applying tosaid third light valve illumination light that is reflected by saidcolor separation function element and that passes though an additionalpolarization separation element, and image light reflected from saidthird light valve is separated from said illumination light by saidadditional polarization separation element so as to generate image lightcorresponding to a third color; and e) further combining combined imagelight corresponding to both the first color and the second color withthe image light corresponding to the third color so that the color imagelight can be generated, wherein, said first light valve, said secondlight valve, and said third light valve are reflective light valves thatcontrol polarization directions.
 9. The method of imaging as claimed inclaim 8, wherein, said color separation function element and saidpolarization direction changing element configuring said first colorseparation member, said polarization separation element, said additionalpolarization separation element, and said color combining element arearranged in the form of a cross.
 10. The method of imaging as claimed inclaim 7, wherein, an additional polarization direction changing elementis provided on an outgoing optical path of the color image lightgenerated by said color combining element so as to make polarizationdirections of the image light corresponding to the first color, thesecond color, and the third color in the color image light coincide withone another.
 11. A method of imaging, said method comprising the stepsof: a1) making linearly polarized light first incident on a first colorseparation member of a color separation device at an angle ofapproximately 45 degrees so as to separate the linearly polarized lightinto reflected light and transmitted light, both reflected light andtransmitted light having different colors and one of the differentcolors corresponding to one of three colors; a2) making one of thereflected light and the transmitted light being made incident on asecond color separation member of said color separation device so as toseparate said one of the reflected light and the transmitted light intofurther reflected light and further transmitted light, both furtherreflected light and further transmitted light corresponding to the othertwo of the three colors, respectively; b1) receiving by a first lightvalve, a second light valve, and a third light valve, respectively, oneof the three colors separated from the linearly polarized light by saidcolor separation device; b2) generating by said first light valve, saidsecond light valve, and said third light valve, respectively, imagelight corresponding to said one of the three colors; c) combining by acolor combining element image lights formed with each of the threecolors at said first light valve, said second light valve, and saidthird light valve, respectively, so that color image light can begenerated; d1) applying to said first light valve illumination lightthat passes through said color separation function element and saidpolarization direction changing element, respectively, and that isreflected by said polarization separation element, and image lightreflected from said first light valve is separated from the illuminationlight by said polarization separation element so as to generate imagelight corresponding to a first primary light; d2) applying to saidsecond light valve illumination light that passes through said colorseparation function element, said polarization direction changingelement, and said polarization separation element, respectively, andimage light reflected from said second light valve is separated from theillumination light by said polarization separation element so as togenerate image light corresponding to a second color, the image lightcorresponding to the first color and the image light corresponding tothe second color are also combined by said polarization separationelement; d3) applying to said third light valve illumination light thatis reflected by said color separation function element and that passesthough an additional polarization separation element, and image lightreflected from said third light valve is separated from saidillumination light by said additional polarization separation element soas to generate image light corresponding to a third color; and e)further combining combined image light corresponding to both the firstcolor and the second color with the image light corresponding to thethird color so that the color image light can be generated, wherein,said first color separation member has a color separation functionelement that reflects or transmits incident light of a certain color anda polarization direction changing element that changes polarizationdirections of different predetermined wavebands of the incident light indifferent modes, said second color separation member has a polarizationseparation element, said first light valve, said second light valve, andsaid third light valve are reflective light valves that controlpolarization directions, said color separation function element and saidpolarization direction changing element configuring said first colorseparation member, said polarization separation element, said additionalpolarization separation element, and said color combining element arearranged on orthogonal inclined surfaces of each of four right-angleprisms, and said color separation function element and said polarizationdirection changing element configuring said first color separationmember, said polarization separation element, said additionalpolarization separation element, and said color combining element areintegrated in the form of a block.
 12. A method of imaging, said methodcomprising the steps of: a1) making linearly polarized light firstincident on a first color separation, member of a color separationdevice at an angle of approximately 45 degrees so as to separate thelinearly polarized light into reflected light and transmitted light,both reflected light and transmitted light having different colors andone of the different colors corresponding to one of three colors; a2)making one of the reflected light and the transmitted light being madeincident on a second color separation member of said color separationdevice so as to separate said one of the reflected light and thetransmitted light into further reflected light and further transmittedlight, both further reflected light and further transmitted lightcorresponding to the other two of the three colors, respectively; b1)receiving by a first light valve, a second light valve, and a thirdlight valve, respectively, one of the three colors separated from thelinearly polarized light by said color separation device; b2) generatingby said first light valve, said second light valve, and said third lightvalve, respectively, image light corresponding to said one of the threecolors; c) combining by a color combining element image lights formedwith each of the three colors at said first light valve, said secondlight valve, and said third light valve, and respectively, so that colorimage light can be generated, wherein, said first color separationmember has a color separation function element that reflects ortransmits incident light of a certain color and a polarization directionchanging element that changes polarization directions of differentpredetermined wavebands of the incident light in different modes, saidsecond color separation member has a polarization separation element,and a polarizer detachably provided at the end of an outgoing opticalpath of the color image light generated by said color combining element.13. A method of projection, said method comprising the steps of: a1)making linearly polarized light first incident on a first colorseparation member of a color separation device at an angle ofapproximately 45 degrees so as to separate the linearly polarized lightinto reflected light and transmitted light, both reflected light andtransmitted light having different colors and one of the differentcolors corresponding to one of three colors; a2) making one of thereflected light and the transmitted light incident on a second colorseparation member of said color separation device so as to separate saidone of the reflected light and the transmitted light into furtherreflected light and further transmitted light, both further reflectedlight and further transmitted light corresponding to the other two ofthe three colors, respectively; b1) receiving by a first light valve, asecond light valve, and a third light valve, respectively, one of thethree colors separated from the linearly polarized light by said colorseparation device; b2) generating by said first light valve, said secondlight valve, and said third light valve, respectively, image lightcorresponding to said one of the three colors; c) combining by a colorcombining element the image lights formed with each of the three colorsat said first light valve, said second light valve, and said third lightvalve, respectively, so that color image light can be generated; f1)generating the color image light corresponding to the three colors; andf2) projecting said color image light onto a screen by a projectionlens, wherein, said first color separation member has a firstpolarization direction changing element, a second polarization directionchanging element, each of said polarization direction changing elementchanging polarization directions of different predetermined wavebands ofincident light in different modes, and a first polarization separationelement that reflects or transmits the incident light according to thepolarization directions of the incident light, said second colorseparation member has a second polarization separation element, and saidfirst polarization separation element is supported between said firstpolarization direction changing element and said second polarizationdirection changing element.
 14. A method of projection, said methodcomprising the steps of: a1) making linearly polarized light firstincident on a first color separation member of a color separation deviceat an angle of approximately 45 degrees so as to separate the linearlypolarized light into reflected light and transmitted light, bothreflected light and transmitted light having different colors and one ofthe different colors corresponding to one of three colors; a2) makingone of the reflected light and the transmitted light incident on asecond color separation member of said color separation device so as toseparate said one of the reflected light and the transmitted light intofurther reflected light and further transmitted light, both furtherreflected light and further transmitted light corresponding to the othertwo of the three colors, respectively; b1) receiving by a first lightvalve, a second light valve, and a third light valve, respectively, oneof the three colors separated from the linearly polarized light by saidcolor separation device; b2) generating by said first light valve, saidsecond light valve, and said third light valve, respectively, imagelight corresponding to said one of the three colors device; c) combiningby a color combining element image lights formed with each of the threecolors at said first light valve, said second light valve, and saidthird light valve, respectively, so that color image light can begenerated; f1) generating the color image light corresponding to thethree colors; and f2) projecting said color image light onto a screen bya projection lens, wherein, said first color separation member has acolor separation function element that reflects or transmits incidentlight of a certain color and a polarization direction changing elementthat changes polarization directions of different predeterminedwavebands of the incident light in different modes, said second colorseparation member has a polarization separation element, said colorseparation function element is provided on an inclined surface of afirst optical prism, said polarization direction changing element isprovided on a first inclined surface of a second optical prism, saidpolarization separation element is provided on a second inclined surfaceof the second optical prism, and said first optical prism and saidsecond optical prism are arranged so that said color separation functionelement faces in parallel with said polarization direction changingelement.
 15. A method of color separation, said method comprising thesteps of: a1) making linearly polarized light first incident on a firstcolor separation member at an angle of approximately 45 degrees so as toseparate the linearly polarized light into reflected light andtransmitted light, both reflected light and transmitted light havingdifferent colors and one of the different colors corresponding to one ofthree colors; and a2) making one of the reflected light and thetransmitted light incident on a second color separation member so as toseparate said one of the reflected light and the transmitted light intofurther reflected light and further transmitted light, both furtherreflected light and further transmitted light corresponding to the othertwo of the three colors, respectively, wherein, said first colorseparation member has a first polarization direction changing element, asecond polarization direction changing element, each of saidpolarization direction changing element changing polarization directionsof different predetermined wavebands of incident light in differentmodes, and a first polarization separation element that reflects ortransmits the incident light according to the polarization directions ofthe incident light, and said second color separation member has a secondpolarization separation element
 16. The method of color separation asclaimed in claim 15, wherein, said first polarization separation elementis supported between said first polarization direction changing elementand said second polarization direction changing element.
 17. A method ofcolor separation, said method comprising the steps of: a1) makinglinearly polarized light incident on a first color separation member atan angle of approximately 45 degrees so as to separate the linearlypolarized light into reflected light and transmitted light, bothreflected light and transmitted light having different colors and one ofthe different colors corresponding to one of three colors; and a2)making one of the reflected light and the transmitted light incident ona second color separation member so as to separate said one of thereflected light and the transmitted light into further reflected lightand further transmitted light, both further reflected light and furthertransmitted light corresponding to the other two of the three colors,respectively, wherein, said first color separation member has a firstpolarization direction changing element, a second polarization directionchanging element, each of said polarization direction changing elementchanging polarization directions of different predetermined wavebands ofincident light in different modes, and a first polarization separationelement that reflects or transmits the incident light according to thepolarization directions of the incident light; and said second colorseparation member has a second polarization separation element, wherein,said method further comprising the steps of: a3) making the linearlypolarized light incident on and pass through said first polarizationdirection changing element at an angle of approximately 45 degrees so asto separate the linearly polarized light into waveband light having itspolarization direction changed and waveband light not having itspolarization direction changed; a4) reflecting the waveband light havingits polarization direction changed by said first polarization directionchanging element from said first polarization separation element as thereflected light corresponding to one of the three colors; a5) passingthe waveband light not having its polarization direction changed by saidfirst polarization direction changing element through said firstpolarization separation element as the transmitted light; a6) separatingthe reflected light from the transmitted light by passing through saidfirst polarization direction changing element again; a7) passing thetransmitted light through said second polarization direction changingelement that is provided in parallel with said first polarizationdirection changing element so as to separate the transmitted light intowaveband light having its polarization direction changed and wavebandlight not having its polarization direction changed; a8) reflecting thewaveband light having its polarization direction changed by said secondpolarization direction changing element from said second polarizationseparation element as further reflected light corresponding to one ofthe other two of the three colors; and a9) passing the waveband lightnot having its polarization direction changed by said secondpolarization direction changing element through said second polarizationseparation element as further transmitted light corresponding to theother one of the other two of the three colors.
 18. A method of colorseparation, said method comprising the steps of: a1) making linearlypolarized light incident on a first color separation member at an angleof approximately 45 degrees so as to separate the linearly polarizedlight into reflected light and transmitted light, both reflected lightand transmitted light having different colors and one of the differentcolors corresponding to one of three colors; and a2) making one of thereflected light and the transmitted light incident on a second colorseparation member so as to separate said one of the reflected light andthe transmitted light into further reflected light and furthertransmitted light, both further reflected light and further transmittedlight corresponding to the other two of the three colors, respectively,wherein, said first color separation member has a first polarizationdirection changing element, a second polarization direction changingelement, each of said polarization direction changing element changingpolarization directions of different predetermined wavebands of incidentlight in different modes, and a first polarization separation elementthat reflects or transmits the incident light according to thepolarization directions of the incident light, and said second colorseparation member has a second polarization separation element, wherein,said method further comprising the step of: a3) optically integrating afirst combined optical element and a second combined optical element sothat said first polarization separation element adheres to said secondpolarization direction changing element, wherein, said first combinedoptical element has said first polarization direction changing elementadhesively provided on an inclined surface of a first optical prism andsaid first polarization separation element stacked on said firstpolarization direction changing element, and said second combinedoptical element has said second polarization separation elementadhesively provided on one of two orthogonal inclined surfaces of asecond optical prism and said second polarization direction changingelement adhesively provided on the other one of the two orthogonalinclined surfaces of the second optical prism.
 19. A method of colorseparation, said method comprising the steps of: a1) making linearlypolarized light first incident on a first color separation member at anangle of approximately 45 degrees so as to separate the linearlypolarized light into reflected light and transmitted light, bothreflected light and transmitted light having different colors and one ofthe different colors corresponding to one of three colors; and a2)making one of the reflected light and the transmitted light incident ona second color separation member so as to separate said one of thereflected light and the transmitted light into further reflected lightand further transmitted light, both further reflected light and furthertransmitted light corresponding to the other two of the three colors,respectively, wherein, said first color separation member has a colorseparation function element that reflects or transmits incident light ofa certain color and a polarization direction changing element thatchanges polarization directions of different predetermined wavebands ofthe incident light in different modes, said second color separationmember has a polarization separation element, said color separationfunction element is provided on an inclined surface of a first opticalprism, said polarization direction changing element is provided on afirst inclined surface of a second optical prism, said polarizationseparation element is provided on a second inclined surface of thesecond optical prism, and said first optical prism and said secondoptical prism are arranged so that said color separation functionelement faces in parallel with said polarization direction changingelement.
 20. The method of color separation as claimed in claim 19,wherein, said color separation function element is provided in parallelwith said polarization direction changing element.
 21. The method ofcolor separation as claimed in claim 19, wherein said method furthercomprising the steps of: a3) making the linearly polarized lightincident on said color separation function element at an angle ofapproximately 45 degrees so as to separate the linearly polarized lightinto reflected light and transmitted light, both reflected light andtransmitted light having different colors and one of the differentcolors corresponding to one of the three colors; a4) making one of thereflected light and the transmitted light passes through saidpolarization direction changing element so as to separate said one ofthe reflected light and the transmitted light into waveband light havingits polarization direction changed and waveband light not having itspolarization direction changed; a5) reflecting the waveband light havingits polarization direction changed by said polarization directionchanging element from said polarization separation element as reflectedlight corresponding to one of the other two of the three colors; and a6)passing the waveband light not having its polarization direction changedby said polarization direction changing element through saidpolarization direction changing element as transmitted lightcorresponding to the other one of the other two of the three colors. 22.A method of color separation, said method comprising the step of: a)making linearly polarized light first incident on a color separationmember at an angle of approximately 45 degrees so as to separate thelinearly polarized light into reflected light and transmitted light,both reflected light and transmitted light having different colors andone of the different colors corresponding to one of three colors,wherein, said color separation member comprising a first polarizationdirection changing element, a second polarization direction changingelement, each of said polarization direction changing elements changingpolarization directions of different predetermined wavebands of incidentlight, and a polarization separation element that reflects or transmitsthe incident light according to polarization directions of the incidentlight, and said polarization separation element is supported betweensaid first polarization direction changing element and said secondpolarization direction changing element.
 23. The method of colorseparation as claimed in claim 22, wherein, said first polarizationdirection changing element and said second polarization directionchanging elements are wavelength selective retarders.
 24. A method ofcolor separation, said method comprising the step of: a) making linearlypolarized light first incident on a color separation member at an angleof approximately 45 degrees so as to separate the linearly polarizedlight into reflected light and transmitted light, both reflected lightand transmitted light having different colors and one of the differentcolors corresponding to one of three colors, wherein, said colorseparation member comprising a color separation function element whichreflects or transmits incident light of a certain color, and apolarization direction changing element that changes polarizationdirections of different predetermined wavebands of the incident light,said color separation function element is provided in parallel with saidpolarization direction changing element; said color separation functionelement is provided on an inclined surface of a first optical prism,said polarization direction changing element is provided on a firstinclined surface of a second optical prism, a polarization separationelement is provided on a second inclined surface of the second opticalprism, and said first optical prism and said second optical prism arearranged so that said color separation function element faces inparallel with said polarization direction changing element.
 25. Themethod of color separation as claimed in claim 24, wherein, saidpolarization direction changing element is a wavelength selectiveretarder.